/*
 * Copyright 2010 The Apache Software Foundation
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase.coprocessor;

import org.apache.hadoop.hbase.ipc.CoprocessorProtocol;
import java.io.IOException;

/**
 * A sample protocol for performing aggregation at regions.
 */
public interface ColumnAggregationProtocol extends CoprocessorProtocol {
  /**
   * Perform aggregation for a given column at the region. The aggregation
   * will include all the rows inside the region. It can be extended to
   * allow passing start and end rows for a fine-grained aggregation.
   * @param family family
   * @param qualifier qualifier
   * @return Aggregation of the column.
   * @throws exception.
   */
  public long sum(byte[] family, byte[] qualifier) throws IOException;
}